% -> switches $ back to its original definition
\IfPackagesLoaded{onlyamsmath,tabu}{%
  \RequirePackage{etoolbox}
  \AtBeginEnvironment{tabu}{\catcode`$=3 } 
}{}
% thanks to egreg for providing this fix.
% The discussion on why this is necessary can be read at
% http://tex.stackexchange.com/questions/35139/restore-original-definition-of